System comprising two or more pumps connected in parallel and a pressure switch conceived to operate in said system

ABSTRACT

System with two pumps (B 1,  B 2 ) connected in parallel to a delivery manifold ( 1 ) and respective electronic pressure switches (P 1,  P 2 ) provided with a pressure sensor (S 1,  S 2 ) connected to the delivery manifold ( 1 ) and designed to alternate their operation between a first configuration with a first shut-down pressure (Pmax 1 ) and a first start-up pressure (Pmin 1 ) and a second configuration with a second shut-down pressure (Pmax 2 ) and a second start-up pressure (Pmin 2 ), the first shut-down pressure (Pmax 1 ) being greater than the second shut-down pressure (Pmax 2 ) and the first start-up pressure (Pmin 1 ) greater than the second start-up pressure (Pmin 2 ). Each of the pressure switches (P 1,  P 2 ) is designed to alternate their operation between the two configurations according to a pressure reading (Pimp) at the delivery manifold by the pressure sensor(s) (S 1,  S 2 ). The invention also relates to a pressure switch.

FIELD OF THE INVENTION

The present invention relates to the control of a pressure groupprovided with two or more pumps and their respective pressure switches,and aims to ensure optimal control and lifespan of the system.

BACKGROUND OF THE INVENTION

Systems equipped with two or more pumps connected in parallel and adelivery manifold to which the pump outputs are connected, whichcomprises respective pressure switches provided with means for measuringthe pressure in the delivery manifold to control the operation of eachpump, are known. In the case of mechanical pressure switches, thepressure is detected mechanically in the pressure switch itself, whilein the case of an electronic pressure switch, it comprises a pressuresensor and an actuation relay.

These systems are designed to meet the demand when it has consumptionpeaks, since it is more efficient in terms of operations and costs tohave two smaller pumps, which can operate in optimal conditions, insteadof one that would be underused most of the time.

This implies, however, greater needs in terms of control.

In particular, it must be foreseen that the pressure switches havedifferent start-up/shut-down pressure configurations, and in particular,it is necessary that one of the pumps has a first start-up pressure anda first shut-down pressure, while the other has a second start-uppressure and a second shut-down pressure, the first shut-down pressurebeing greater than the second shut-down pressure and the first start-uppressure being greater than the second start-up pressure, as shown inFIG. 1.

As is known, pumps usually operate with a boiler also connected to thedelivery manifold, and the different shut-down/start-up pressures ensurethe stability of the system.

What happens is the following. It is assumed that the system is at restat a pressure comprised between the upper shut-down pressure (Pmax1) ofthe pumps and the upper start-up pressure (Pmin1). When a water demandoccurs, the pressure in the delivery manifold begins to drop. By havinga boiler, the pressure drop is gentler than if did not exist. When thefirst start-up pressure is reached (Pmin1), the first pump is starts tooperate.

Then it may happen that the flow rate of this first pump is higher thanthe consumption that has caused its start-up, so that the pressure inthe delivery tends to increase, the boiler is refilled, and theshut-down pressure of the first bomb is reached. In other words, whathappens is what would occur if there were only one pump and the secondpump did not start to operate (FIG. 2).

Or it may happen that the flow of the first pump is not sufficient tosatisfy the demand and that the pressure continues to fall until thesecond start-up pressure (Pmin2) is reached, such that the second pumpstarts to operate. In this case, if the system is correctly sized torespond to the demand peaks, the two pumps can satisfy the demand andre-fill the boiler. During the rise of the pressure in the manifold, thesecond shut-down pressure (Pmax2) will be reached first, at which timethe second pump will shut down, and then the first shut-down pressure(Pmax1) will be reached, at which time the first pump will also shutdown. This sequence is illustrated in FIG. 3.

The system just described, in which both mechanical and electronicpressure switches can be used, involves a very simple programming, byestablishing the four pressure limits.

However, it has the obvious disadvantage that the first pump will workmuch more often than the other, which means that the system is notoptimal in consideration of the life of the components, since the firstpump will most likely fail long before the second.

In order to respond to this drawback, two solutions have been proposed,the first consisting of connecting the pumps or the pressure switches toa common plant and the second involving the use of independentelectronic pressure switches equipped with means of communicationbetween each other. Both solutions are complex, since the first involveshaving a plant for synchronisation, while the other involves connectingthe pressure switches to each other. With both systems it is possible toalternate the pump configurations so that they end up supporting asimilar workload.

The inventors consider that these solutions are expensive.

Two-pump systems are also known, one is a duty pump and the other astandby pump where one of the pumps acts as a standby pump in case offailure of the duty pump. It is a configuration in which they are becomeoperational simultaneously. These systems have the disadvantage that themain pump ages and the standby pump remains without operating for a longtime.

As a solution to this problem, enabling the system to alternate througha common plant so that the duty and standby pumps alternate in eachoperating cycle or in scheduled periods of time is known.

The inventors consider that this solution is expensive, since itinvolves the incorporation of a control plant of the two pumps.

DESCRIPTION OF THE INVENTION

In order to respond to the shortcomings of the state of the art, thepresent invention proposes a system comprising at least two pumpsconnected in parallel, a delivery manifold to which the outputs of thetwo or more pumps are connected, which comprises respective electronicpressure switches provided with a pressure sensor connected to thedelivery manifold to control the operation of each pump, wherein thepressure switches are configured to alternate their operation between atleast two start-up and shut-down pressure configurations, namely:

-   -   a first configuration with a first shut-down pressure and a        first start-up pressure;    -   a second configuration with a second shut-down pressure and a        second start-up pressure;

wherein the first shut-down pressure is greater than the secondshut-down pressure and wherein the first start-up pressure is greaterthan the second start-up pressure, wherein the pressure switches areconfigured to perform said alternation according to a pressure readingof the delivery manifold with the pressure sensor(s).

By means of these features, it is possible to properly alternate theoperation of two or more pumps, and ensure that each one of them has asimilar accumulated workload, with which the lifespan of the system isincreased. With respect to what is known, a system based oncommunication between pressure switches is substituted, whether or notan intermediate plant is used, by a system based on the monitoring ofthe common pressure along with the knowledge of the operating status ofeach pump for its corresponding pressure switch.

In particular, in the case of two pumps, each pressure switch willalternate its operation between the first and second shut-down andstart-up pressures.

This concept substantially improves what is disclosed, for example, inU.S. Pat. No. 4,444,545, wherein a two-pump system coordinated by acommon control device is described. In contrast, according to thepresent invention, no control centre is needed, since each pressureswitch is equipped with a pressure sensor, such that from a pressurereading it is possible to know the system status parameters that need tobe known.

In some embodiments, the pressure switches are configured to be put inthe first configuration or in the second configuration when the pressuresensor indicates that the first shut-down pressure has been exceeded apredetermined number of times. In this way, if for any reason one of thepumps is started for a minimum number of consecutive times, the systemwill automatically assign the system a status that will enable thealternation between pumps to be restarted. In other words, if for somereason, for example due to errors in the pressure measurements, or dueto pressures close to the threshold pressures, the two pumps begin tooperate simultaneously with the same mode, when it is detected that oneof them exceeds a number of consecutive start-ups, then it willestablish which one will work with which pressure limits. The pressureswitch that decides these situations will be designated as master, andthe other as slave. Obviously, it is envisaged that the pressureswitches, when configured after installation, can be programmed as amaster or as a slave.

In some embodiments, the system comprises a boiler connected to thedelivery manifold. In the vast majority of cases, as usual, the systemwill have a boiler, which allows the differences between the thresholdpressures to significantly increase, and therefore avoid theuninterrupted start-up and shut-down of the pumps.

In some embodiments, each of the pressure switches is provided with apressure sensor.

In some embodiments, the system comprises a common housing of the twopressure switches. In other words, the provision of the pressureswitches in the system as separate units can be envisaged, which will bethe most usual, or they can be provided integrated in a single housing,which will facilitate the installation thereof. In this case, it canalso be foreseen that the programming is simpler, since the deviceitself can already decide which is the master unit.

The invention also relates to a pressure switch intended to beintegrated in a system according to any of the variants described, andwhich is configured to alternate its operation between twoconfigurations of shut-down and start-up pressure:

-   -   a first configuration with a first shut-down pressure and a        first start-up pressure;    -   a second configuration with a second shut-down pressure and a        second start-up pressure;

wherein the first shut-down pressure is greater than the secondshut-down pressure and wherein the first start-up pressure is greaterthan the second start-up pressure, wherein the pressure switch isconfigured to perform said alternation according to a pressure readingof the delivery manifold with the pressure sensor.

The invention also relates to a system comprising two pumps connected inparallel, a drive manifold to which the outputs of the two pumps areconnected, comprising electronic pressure switches provided withpressure sensors connected to the delivery manifold to control theoperation of each pump, wherein the two pressure switches are configuredwith the same shut-down and start-up pressure, one of the electronicpressure switches being configured to operate as a master and the otherelectronic pressure switch being configured to operate as a slave,having the electronic pressure switch configured to operate as a masterwith a synchronisation pressure different than the synchronisationpressure of the electronic pressure switch configured to operate as aslave, the synchronisation pressures being lower than the start-uppressure, so that it is possible to return to an alternating operationconfiguration between pumps when the alternating configuration is lost.

With these features, it is possible to have a system that ensures analternating operation, wherein only one or the other pump is inoperation, without needing to have a control centre connected to the twopumps, or to the two pressure switches; instead, it is possible toensure the alternation with only the pressure reading of the deliverymanifold.

The asymmetry in the so-called synchronisation pressures are those thatensure re-synchronisation in case of the loss of synchronisation.

BRIEF DESCRIPTION OF THE FIGURES

To complement the description and for the purpose of aiding to betterunderstand the features of the invention according to a practicalexemplary embodiment thereof, a set of figures is attached as anintegral part of the description in which the following has beendepicted with an illustrative and non-limiting character:

FIG. 1 is a schematic diagram showing the relationship between thestart-up and shut-down pressures of two pumps arranged to operate inparallel.

FIG. 2 shows the time evolution of the pressure in a sequence in which asingle pump is started.

FIG. 3 shows the time evolution of the pressure in a sequence in whichthe two pumps are started.

FIG. 4 shows the time evolution of the pressure in a sequence in whichthe two pumps are started and the auxiliary pump is stopped andsuccessively starts up due to variations in consumption.

FIG. 5 shows a diagram of the installation provided with two pumps.

FIGS. 6a and 6b show diagrams of embodiments in which the two pressureswitches are in the same housing, to facilitate the installationthereof.

FIG. 7 shows the configuration pressures and the relative value thereofin the case of a system of two pumps arranged to operate in purealternation.

FIGS. 8 and 9 show diagrams of time evolution of the pressure.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

As can be seen in FIG. 5, according to a preferred embodiment, theinvention relates to a system S comprising two pumps B1, B2 connected inparallel, a delivery manifold 1 to which the outputs of the two pumpsB1, B2 are connected, and comprising respective electronic pressureswitches P1, P2 to control the operation of each pump B1, B2. The systemis completed with a boiler 2 intended to ensure a greater stability inthe pressure, such as for example a membrane boiler.

Each pressure switch is provided with a pressure sensor S1, S2 connectedto the delivery manifold 1, so that they can measure the same pressure,or at most a pressure that will differ in the pressure loss between thetwo pressure points, if they are different. Obviously, we will try toensure that the difference is minimal to ensure the correct operation ofthe system.

In particular, the pressure switches P1, P2 are configured to alternatetheir operation between two or more start-up pressure configurationsPmax1, Pmax2 and shut-down pressures Pmin1, Pmin2:

-   -   a first configuration with a first shut-down pressure Pmax1 and        a first start-up pressure Pmin1;    -   a second configuration with a second shut-down pressure Pmax2        and a second start-up pressure Pmin2.

Therefore, each one of them will alternate their status between said twointervals. It should be noted that the numbering 1, 2 after thepressures does not imply that they are associated with one of thepressure switch pump groups, but on the contrary, each of the pumps willalternate its operation between these configurations, as will beclarified in the following.

As can be seen in FIG. 1, the first shut-down pressure Pmax1 is greaterthan the second shut-down pressure Pmax2 and the first start-up pressurePmin1 is greater than the second start-up pressure Pmin2, which is knownin the state of the art.

However, the novelty lies in that the pressure switches P1, P2 areconfigured to carry out said alternation according to a pressure readingPimp in the delivery manifold with the pressure sensor(s) S1, S2.

During the initial configuration of the group, one of the pressureswitches must be designated as master. This pressure switch will beresponsible for managing the resynchronisation algorithms. The otherpressure switch, or the others if the system comprises more than two,will be designated as slave.

As for the order of start-up of the pumps, the pump that operatesbetween Pmax1 and Pmin1 is defined as the main one. The pump thatoperates between Pmax2 and Pmin2 is defined as auxiliary. If there weremore auxiliary pumps, they would be defined following this logic.

During operation, both the master device and the slave/slaves canoperate as main pump or auxiliary pump(s) due to alternating.

The initial configuration, in a group of two pumps, consists in that thefirst pump B1 has the status of operating with the first shut-downpressure Pmax1 and the first start-up pressure Pmin1 (master deviceoperating as main) and the second pump has the status of operating withthe second shut-down pressure Pmax2 and the second start-up pressurePmin2 (slave device operating as auxiliary), the first shut-downpressure Pmax1 being greater than the second shut-down pressure Pmax2and the first start-up pressure Pmin1 being greater than the secondstart-up pressure Pmin2. For example, Pmax1=3.5 bar, Pmin1=2.5 bar,Pmax2=3 bar and Pmin2=2 bar.

This may lead to the cases that are detailed below.

Case 1:

As can be seen in FIG. 2, first the pressure in the delivery manifold 1falls below Pmin1, which corresponds to t1. This causes the activationof the pump B1. If B1 has sufficient capacity, the pressure in themanifold will rise to Pmax1, and then B1 will shut down.

What constitutes the novelty of the invention is that the secondpressure switch P2, associated with B2, will have monitored the pressurein the manifold and will have verified that the pressure has risen toPmax1. Therefore, it will be possible to know which should be the firstto start up in the next cycle. Moreover, the first pressure switch P1will know that the pressure Pmax1 with B1 in operation has been reached.Then it will be possible to know which should be the second to start up,if necessary. The change of status configurations is represented byarrow B1⇄B2 at time t2.

Case 2:

If the first pump B1 has no capacity, the pressure will continue todecrease until Pmin2, moment (t2) when pump B2 will be activated. Thenthe pressure rises again and if the added flow is sufficient, firstPmax2 (time t3) will be reached, and the second pump B2 will shut down,B1 will continue working until reaching Pmax1, moment (time t4) when B1will shut down. At the top of each time interval it is indicated whichpumps are activated. This sequence corresponds to the case known andshown in FIG. 3.

Again, what constitutes the novelty of the invention is that the secondpressure switch P2, associated with B2, will have monitored the pressurein the manifold and will have verified that the pressure has risen toPmax1. Therefore, it will be possible to know which should be the firstto start up in the next cycle. Moreover, the first pressure switch P1will know that the pressure Pmax1 with B1 in operation has been reached.Then it will be possible to know which should be the second to start up,if necessary. The change of status configurations is represented byarrow B1⇄B2 at time t4.

Therefore, the pressure switches can be synchronised based on theknowledge of the pressure read in the manifold and the knowledge of itsoperating status. Therefore, it is not necessary according to theinvention to use a plant or a communication system between pressureswitches, but synchronisation is performed by reading a common pressure.

Case 3:

Starting from the situation of case 2 after time t3 (B2 shut down), ifthe demand reverses its course and increases again until the pressuredrops below Pmin2, pump 2 starts up again as happens at times t2.n. Thissituation can last until reaching the conditions of time t4. Thissequence corresponds to the case known and shown in FIG. 4, in which theperiod of time in which fluctuations in consumption occur have beenhighlighted.

Case 4:

After completing a cycle in Case 1 or Case 2 and Case 3 the order ofstart-up of the pumps is reversed, that is, the master device will actas auxiliary and the slave device as the main one.

Under these conditions, if the work cycle is carried out under theconditions described in FIG. 2 or FIG. 3, in terms of the sequence ofpressures and with the new order of pumps, there will be no alterationin the logic of normal operation.

Case 5:

Because the decisions associated with the change in the start-up orderare linked to the pressure reading of each device, a margin of tolerancemust be given to said reading in the case that small calibrationdeviations occur.

This tolerance can cause the auxiliary device to misinterpret thestopping of the main device. This would create a change in thealternation causing both devices to work in auxiliary mode(desynchronisation).

To solve this problem the master device, after 2 consecutive start-upsin Pmin2, applies a resynchronisation algorithm.

It is an algorithm that detects N (for example two or three) consecutivestart-ups of the master pump as auxiliary.

In particular, the master pump working as an auxiliary after twoconsecutive start-ups does not shut down in Pmax2 as it wouldcorrespond, but stops in Pmax1, which forces the auxiliary pump toreverse its order and return both to alternating state, that is, as acycle like the one described in FIG. 2.

Although in the above description of preferred embodiments theapplication of the invention to a system provided with two pumps hasbeen described, it is evident that the invention can be applied to alarger number of pumps, with the relevant changes. If, for example,there is a third pump, a third start-up pressure and a third shut-downpressure must be defined. Regarding the alternating algorithms, acyclical strategy will be used, always with the objective of ensuringthe same long-term workload of the three pumps.

Finally, FIGS. 6a and 6b show two embodiments in which the two pressureswitches are presented in a common housing, with two pressure points oronly one.

Up to this point, a system has been described in which there are twopumps that complement each other in order to meet the flow needs, sothat one or both of them work, and in which the one that will work aloneis alternating.

A different solution is described below, with reference to FIGS. 7 to 9,in which the pumps never work simultaneously, but they work in aso-called pure alternating mode, that is, either one works or the otherworks.

As already indicated in the background section, to achieve purealternation, the systems of the state of the art are based on theincorporation of a central control unit that must be connected to bothpumps.

Now, as will be explained below, according to the present invention, itis possible to go without a control centre, because if each of thepressure switches (each pump has one) has a pressure sensor, it ispossible to carry out a two-pump system with pure alternation onlythrough the pressure reading in the common delivery manifold.

For this, a system with two pumps B1 and B2, as in the system describedabove, is once again available. The two pressure switches P1 and P2 areconfigured as master.

At the moment of putting the system into tension, the selected pumpdesignated as master (for example B1) is configured as the first B1 andthe slave as the second B2.

The start-up and shut-down parameters are identical for each equipment,in this case Pmax and Pmin, as shown in the temporary functionsillustrated in FIGS. 8 and 9.

In each cycle, only one pump is started from Pmin to Pmax. In the nextcycle it alternates the start-up with the second pump.

As shown in FIG. 8, the pump that is stopped, in this case B2, reads theline pressure and can know that the first B1 has been started when thepressure has dropped to Pmin and then has gone up to Pmax. With thisinformation it becomes configured as the first for the next cycle. Thepump B1 that has just worked as the first is configured to work as asecond.

However, in order to ensure the correct operation of the system, it isnecessary to define internal safety pressure levels for each equipment:

For the master pump: Psynchro1<Pmin

For the slave pump: Psynchro2<Pmin

Where always Psynchro2<Psynchro1.

We emphasize that the condition of master or slave does not vary, thatis, if B1 is the master it will always be so. The same for B2.

What changes is which pump should be pumped in each cycle, to ensurepure alternation.

The pressures Psynchro1 and Psynchro2 are safety pressures in the casethat there is desynchronisation and the two pumps are configured assecond or in the case that the pump that has to do the first operationis faulty.

The operation is as follows:

If for some reason there is a desynchronisation, and at that moment themain pump (the one that must pump at that moment, for example B2) doesnot pump, then the pressure will fall below Pmin. Therefore, when theline pressure drops so much that Pline<Psynchro1 or Pline<Psynchro2, ifpump B1 is in second mode (i.e. it is the one that is shut down), thenit internally changes its configuration and becomes the first pump (theone that must be started). As the line pressure is lower than Pmin, B1will start automatically.

Therefore, it is possible to return to a normal operating cycle, becausethe pump B1 is the one that pumps, and it will do it until Pmax, thepump B2 remaining shut down. Upon reaching Pmax, the B2 pump will becomethe main pump, which will start up in the next cycle. Pump B1 willbecome the second pump, which should remain shut down in the next cycle.

In other words, if the pump designated at that time as the main one (notto be confused with master) is not operative, the other pump will notstart at Pmin, but will do so at Psynchro1 or Psynchro2 depending onwhether it is the master or slave.

That is, by the asymmetry in the configuration consisting of one beingmaster and the other slave, i.e. the first has Psynchro1>Psynchro2, thesystem can be resynchronised whenever desynchronisation occurs. If thosepressures were equal, that would not be possible.

Another possibility offered by this feature is that if one of the pumpsbreaks down, then the other, only with the reading of pressures, canknow that this has happened and can send an error message.

In this text, the word “comprises” and its variants (such as“comprising”, etc.) should not be understood in an exclusive sense,i.e., they do not exclude the possibility of that which is describedincluding other elements, steps, etc.

Furthermore, the invention is not limited to the specific embodimentsdescribed herein, but rather encompasses the variations that one skilledin the art could make (e.g. in terms of choice of materials, dimensions,components, design, etc.), within the scope of what may be deduced fromthe claims.

1. A system (S) comprising two or more pumps (B1, B2) connected inparallel, a delivery manifold (1) to which the outputs of the two ormore pumps (B1, B2) are connected, which comprises respective electronicpressure switches (P1, P2) equipped with pressure sensors (S1, S2)connected to the delivery manifold (1) to control the operation of eachpump (B1, 82), wherein the pressure switches (P1, P2) are configured toalternate their operation between two or more start-up pressureconfigurations (Pmax1, Pmax2) and shut-down pressure configurations(Pmin1, Pmin2): a first configuration with a first shut-down pressure(Pmax1) and a first start-up pressure (Pmin1); a second configurationwith a second shut down pressure (Pmax2) and a second start-up pressure(Pmin2); wherein the first shut-down pressure (Pmax1) is greater thanthe second shut-down pressure (Pmax2) and wherein the first start-uppressure (Pmin1) is greater than the second start-up pressure (Pmin2),wherein the pressure switches (P1, P2) are configured to perform saidalternation according to a pressure reading (Pimp) of the deliverymanifold with the pressure sensor(s) (S1, S2).
 2. The system accordingto claim 1, wherein the pressure switches (P1, P2) are configured to beput in the first configuration or in the second configuration when thepressure sensor indicates that the first shut-off pressure (Pmax1) hasbeen exceeded by a predetermined number of times (N).
 3. The systemaccording to claim 1, comprising a boiler (2) connected to the deliverymanifold (1).
 4. The system according to claim 1, wherein each of thepressure switches (P1, P2) is provided with a pressure sensor (S1, S2).5. The system according to claim 1, comprising a common housing (A) ofthe two pressure switches (P1, P2).
 6. A pressure switch (P1, P2) foralternating its operation between two configurations of shut-downpressure (Pmax1, Pmax2) and start-up pressure (Pmin1, Pmin2),comprising: a first configuration with a first shut-down pressure(Pmax1) and a first start-up pressure (Pmin1); a second configurationwith a second shut-down pressure (Pmax2) and a second start-up pressure(Pmin2); wherein the first shut-down pressure (Pmax1) is greater thanthe second shut-down pressure (Pmax2) and wherein the first start-uppressure (Pmax1) is greater than the second start-up pressure (Pmax2),wherein the pressure switch (P1, P2) is configured to perform thisalternation according to a pressure reading (Pimp) in the deliverymanifold with the pressure sensor (S1, S2) for integrating in a system(S) comprising two or more pumps (B1, B2) connected in parallel, adelivery manifold (1) to which the outputs of the two or more pumps (B1,B2) are connected, the pressure sensors (S1, S2) being connected to thedelivery manifold (1) to control the operation of each pump (B1, 62). 7.A system (S) comprising: two pumps (B1, B2) connected in parallel, adelivery manifold (1) to which the outputs of the two pumps (B1, B2) areconnected, which comprises respective electronic pressure switches (P1,P2) provided with pressure sensors (S1, S2) connected to the deliverymanifold (1) to control the operation of each pump (B1, B2), wherein thetwo pressure switches (P1, P2) are configured with the same shut-downpressure (Pmax) and start-up pressure (Pmin), one of the electronicpressure switches (P1) being configured to operate as master and theother electronic pressure switch (P2) configured to operate as a slave,wherein the electronic pressure switch (P1) is configured to operate asa master with a synchronization pressure (Psynchro1) different from thesynchronization pressure (Psynchro2) of the electronic pressure switch(P2) configured to operate as a slave, and wherein the synchronizationpressures (Psynchro1, Psynchro2) are lower than the start-up pressure(Pmin) for returning to a configuration of alternating operation betweenpumps when alternating configuration is lost.
 8. The system according toclaim 2, comprising a boiler (2) connected to the delivery manifold (1).9. The system according to claim 2, wherein each of the pressureswitches (P1, P2) is provided with a pressure sensor (S1, S2).